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 GMC-80 SCREAM		  New Topic  Reply to Topic
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ENIGMA6

USA
15 Posts
Posted - 09/23/2011 :  06:49:58  Show Profile  Reply with Quote
I am attempting to use a Russian SBT-9 [alpha/beta/gamma sensitive] tube but all the GMC-80 will do is scream. Is the default voltage too high for this tube? Any suggestions?
Reply #1

Odiez1

73 Posts
Posted - 09/23/2011 :  09:41:28  Show Profile  Reply with Quote
Do you mean by "default voltage" that it's turned all the way down?
Maybe there's some other factor involved..
You should try the mod from the "Probe Modifications" thread, adding the 104 (.1uF) capacitor to C2. That cleared up the "screaming effect" on my 080.
http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=3403

Also, I found some specs on the SBT-9 and it looks like the 080 should work fine with it.
www.gstube.com/data/3004/
Good luck!
-Odie
Edited by - Odiez1 on 09/23/2011 10:39:40
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Reply #2

ENIGMA6

USA
15 Posts
Posted - 09/23/2011 :  15:30:25  Show Profile  Reply with Quote
Thanks for the information. I'll first try turning down the factory voltage [400v] setting to around 300v. If that doesn't fix it I'll try the capacitor mod. I appreciate the link to the specs data. Wasn't aware that page exhisted.
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Reply #3

ENIGMA6

USA
15 Posts
Posted - 09/23/2011 :  16:01:42  Show Profile  Reply with Quote
I turned down the voltage from the factory 405v to 290 which appears to be midange for this tube, seems to work ok now. No screaming except the continous clicking when I place an Americium 241 button in front of the alpha window. Thanks
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